1. Field of the Invention
This invention is directed to a preparation involving Group Ib metals which may be selectively, thermally recrystallized to provide a differentiated color form useful for imaging. In a preferred embodiment, a particulate metastable silver colloid is prepared, which may be subsequently distributed on a substrate, and selectively subjected to thermal energy, to provide a yellow image on a differentiated background.
2. Background of the Prior Art
Defensive Publication T 900,010 describes blue colloidal silver of relatively large particle diameter, which is unstable, and is formed in-situ on a support and subsequently converted to a yellow image on a blue field by the application of halide ions. The halide imaging agent can be transferred from exposed and developed silver halide sources, such as previously developed film, or from an alternative source, such as human skin.
The invention that is the subject of this Defensive Publication by Shuman provides a method for creating distinct yellow images, against a blue background, with minimal difficulty. However, the composition is merely a precursor, requires final preparation on the support itself, and has minimal commercial value. Thus, the Defensive Publication does not describe a practical method for preparing a stable composition which may be used to form a layer on a support and converted, at a later time, nor does it provide a stable preparation which may be subsequently applied to a substrate and imaged. Moreover, the halide chemical imaging process of the Defensive Publication is in many ways constrained, and does not permit the fine control necessary for thermal imaging.
Accordingly, it would be desirable to provide a metastable silver composition which may be selectively converted to provide a yellow image, without the drawbacks and obstacles noted that characterize the prior art.